Polypropylene is excellent in rigidity and heat resistance and therefore is used widely in the field of materials for packaging such as food packaging and fiber packaging. As to the property of packaging materials, the materials are required to be excellent in impact resistance at low temperatures, heat sealability, and antiblocking property in addition to rigidity and heat resistance and also to be excellent in appearance with few fisheyes.
In particular, a packaging material of retortable foods is required to be satisfactory in both heat resistance which is sufficient for withstanding retort sterilization in which high temperature treatment is applied and impact resistance at low temperatures sufficient for withstanding use at low temperatures.
The variety of materials for packaging retortable foods has recently increased and it is required that contents can be checked from the outside. Therefore, packaging materials with excellent transparency have been demanded.
On the other hand, JP 8-169993 A, for example, discloses a polypropylene resin composition having low-temperature impact strength, transparency and slipping property and comprising 51 to 99% by weight of a resin compositions that comprises 1 to 95% by weight of a polypropylene and 5 to 95% by weight of an ethylene-propylene random copolymer having an ethylene content of 10 to 90 mol % and that contains amorphous rubber particles having a diameter of 10 μm or less, and 1 to 49% by weight of a high density polyethylene having a density of 0.935 g/cm3 or more.
JP 10-158463 A discloses a polypropylene film for retorting that comprises 96 to 99 wt % of a propylene-ethylene block copolymer having specific properties and 1 to 4 wt % of a high density polyethylene and that is excellent in impact resistance at low temperatures and also in antiblocking property.
JP 2000-119480 A discloses a propylene resin composition that comprises a propylene-ethylene block copolymer having specific properties and an ethylene-α-olefin copolymer having specific properties and that is balanced in impact resistance at low temperatures, heat seal strength, transparency, resistance to flexural whitening resistance, heat resistance, and so on, and a film for retortable food packaging produced by using the composition.
However, films made of the resin compositions disclosed in these documents are insufficient in appearance, transparency, impact resistance, and anti-blocking property, and there have not found any resin compositions suitable as materials of films for retortable food packaging or films made thereof.
Under such situations, the objective of the present invention is to provide a polypropylene resin composition that is excellent in appearance, transparency, impact resistance and anti-blocking property and suitable as a material of a film for retortable food packaging, and a film made thereof.